Pulverized coal combustion detector

ABSTRACT

The pulverized coal combustion zone at the mouth of each burner of a furnace comprising a number of such units, is viewed by a sensor of molecular carbon radicals, producing a fluctuating output signal when the corresponding burner unit is in operation. Such signal passes through a differential amplifier and line driver to a differential variable preset gain amplifier by way of a capacitor coupling; and from the amplifier to a zero crossing (Schmitt Trigger) detector. The resulting pulsed signal of the detector goes to a monostable multivibrator having a pulse width adjustment. The one-shot output pulses of the multivibrator pass by way of an adjustable slope control on analog integrator of such one-shot pulses, having a DC output of one selected voltage range for actual combustion &#39;&#39;&#39;&#39;ON&#39;&#39;&#39;&#39; and a lower selected voltage range for combustion &#39;&#39;&#39;&#39;OFF&#39;&#39;&#39;&#39;. Such DC voltage output goes to a one-bound comparator, and then through a variable delay circuit to either a Red combustion &#39;&#39;&#39;&#39;ON&#39;&#39;&#39;&#39; or a Green combustion &#39;&#39;&#39;&#39;OFF&#39;&#39;&#39;&#39; lamp.

United States Patent [191 Longrigg I [11 3, 5,25 [451 Apr. 16, 1974 PULVERIZ ED COAL COMBUSTION DETECTOR [75] Inventor: Paul Longrigg, Carrollton, Tex. 73] Assignee: Forney Engineering Company,

' Dallas, Tex.

[22] Filed: July 31, 1972 [21] Appl. No.: 276,872

[52] US. Cl. 340/228.2,250/2l7 F, 328/6, 340/228, 431/79, 431/D1G. 43 [51] Int. Cl. G08b 21/00 [58] Field of Search 340/227, 228, 228.2, 237; 328/6, 2; 431/79, DIG. 43; 250/217 F [56] References Cited UNITED STATES PATENTS 2,834,008 5/1958 Carbauh 340/2282 1 3,513,311 5/1970 McAlister..... 340/228 X 3,716,717 2/1973 Scheidweiter. 340/2282 3,689,773 9/1972 Wheeler 340/2282 X 3,671,953 6/1972 Goldberg 340/227 3,665,440 5/1972 McMenamin..... 340/2282 2,994,859 8/1961 Klein 340/2282 Primary Examiner-John W. Caldwell Assistant ExaminerScott F. Partridge Attorney, Agent, 0r.FirmMarvin A. Naigur; John E. Wilson [57] srR cr The pulverized coal combustion zone at the mouth of each burner of a furnace comprising a number of such units, is viewed by a sensor of molecular carbon-radicals, producing a fluctuating output'signal when the corresponding burner unit is in operation. Such signal passes through a differential amplifier and line driver to a differential variable preset gain amplifier-by way of a capacitor coupling; and from the amplifier to a zero crossing (Schmitt Trigger) detector. The resulting pulsed signal of the detector goes to a monostable multivibrator having a pulse width adjustment. The one-shot-output pulses of the multivibrator pass by way of an adjustable slope control on analog integracomparator, and then through a variable delay circuit to either a Red combustion ON or a Green combustion OFF lamp.

11 Claims, 7 Drawing Figures w n p 1 ma I 3.805258 SHEEY 0F 4 a l I I VARIABLE CONSTANT "sPAcE" "MARK" Fla. 6

REFERENCE- (COMPARISON LEV SIGNAL (FLAME OFF) I 1 PULVERIZED COAL COMBUSTION DETECTOR SUMMARY OF THE INVENTION The frontal area of combustion of a pulverized coal burner in a boiler furnace is scanned by a sensor of molecular carbon radicals in a strategically located probe position. When combustion is present, the sensor produces a fluctuating output, that passes through a differential amplifier and line driver, and then by way of a capacitor and line amplifier, to a zero crossing detector. The output of the latter is amplified and goes to a oneshot multivibrator provided with a pulse width adjustment for optimum burner combustion conditions. The output of the multivibrator passes through an integrator slope control to an analog integrator of the oneshot pulses having a direct current output range of relatively low voltage for flame OFF, and a somewhat higher voltage range for flame ON. Such direct current output is applied to a one-bound comparator, the output of which goes through a variable delay circuit to either a red or a green lamp which corresponds to an ON or.OFF combustion condition, respectively.

By adjusting the slope of the integrator the detector can be adjusted to deal with combustion with low emission, as is present during boiler start-up, or when the burners are operating at low loads. 1 Gas turbulance at any particular burner position is dealt with by varying the time constant of the integrator. In case the integrator time constant cannot be made long enough for any particular situation, then the variable ON-OFF delay is utilized at the output of the comparator. Combustion gas turbulance is a function of the particular burner being viewed, as well as the type of boiler comprising such burner.

Should a particular combustion scintillation content be low in high frequency on account of either the type of coal being burned, or the consistency characteristic of the pulverized coal, then the monostable multivibr ator output pulse width can be-lengthened to compensate therefor. Conversely, the pulse width can be shortened when there is a large amount of high-frequency in the complex scintillation signal of the combustion, and the unit becomes saturated.

In accordance with the present invention the system can be adjusted toindicate OFF/ON conditions for combustion having low emission characteristics, such as those present at boiler start-up, or with burners running at low loads, by virtue of the integrator slope adjustment. Also, undesirable gas turbulance at any particular burner position on a boiler can be dealt with by varying the integrator time constant which can last up to 35-40 seconds, and if the integrator time constant cannot be made long enough for a given situation, the variable ON/OFF delay can be adjusted at the output of the comparator to do so.

BACKGROUND OF THE INVENTION Flame detectors for infrared, visible and ultraviolet radiation are well known; but until the present invention none was suitable for detecting the combustion of pulverized coal in a boiler furnace because of the particular stoichiastic flame front movement of such flames.

One prior system utilized a flame detector having an ultraviolet cell and a silicon photovoltaic cell in a common housing for monitoring the flames of a pulverized coal and oil burner. Such silicon voltaic cell circuit is typical of the prior art, furnishing a signal indicative of the amplitude of the high frequency flicker of the sighted flame and the illumination level thereof. The

output signal and applied them to separate channels. The output signal was first obtained by adjustment of a switch to selected resistors and passed through a coupling capacitor to an AC amplifier. Such output was then increased in voltage by a power amplifier and converted to a DC signal by a demodulator circuit. The DC signal then went to a relay for indicating the ON- OFF condition of the flame.

Some of the general problems relating to pulverize coal flame detection prior to the present invention include the following:

The main problem with all flicker detectors that previously have been used is that they do not cope effectively with the spatial movement of the flame front. This movement is due to turbulence within a furnace and must be considered entirely stoichastic.

The present system uses electronic memory means to solve this spatial variance problem. The memory is centered in the integrator circuit, such that if thehigh frequencies in the flame front move momentarily out of the field of view of the cadmium sulfide sensor, the time constant of the integrator is such as to remember the-flame on condition until the flame front or combustion zone moves back into the field of view of the sensor element.

The instant invention deals with the chemiluminescent molecular carbon radicals formed by coal undergoing combustion at the burner mouth. The first derivative of the signal given off by the short-lived molecular carbon radicals is proportional to the multiple mono-pole acoustic energy generated by the pulverized coal particles undergoing combustion. Thus, detection of light energy from molecular carbon radicals can be correlated with combustion acoustic energy. In the present invention this principle is used to establish the presence or absence of true combustion of pulverized coal particles.

BRIEF DESCRIPTION OF THE DRAWINGS The above brief description as well as further objects, features, and advantages of thev present invention will be more fully appreciated by reference to the following detailed description of a presently preferred but nonetheless illustrative embodiment in accordance with the present invention when taken in connection with the accompanying drawings wherein:

FIG. 1 is a circuit diagram of a pulverized coal flame detector illustrative of the invention;

FIG. 2 is a block diagram of the detector with adjustments shown in more detail;

FIGS. 3 and 4 are graphs corresponding to recordings of voltage wave forms at several points in the system;

FIG. 5 is a representation of the one-shot multivibrator output pulse wave form; and

FIGS. 6 and 7 are graphs of representative recordings of the voltage levels of the comparator input and variable delay output, respectively.

As shown in FIG. 1, a pulverized coal combustion burner mouth area in a boiler 12 containing a number of such areas is viewed or scanned by a cadmium sulfide probe 14 containing a cadmium sulfide sensor 16 comprising a photovoltaic type photo cell. The sensor 16 preferably is a Cd.S.R.C.A Type $02502 sensor head that is connected to a differential amplifier 18 and a line driver 20. The amplified output of the latter is fed to a variable preset gain line amplifier 22 by way of the coupling capacitor 23.

From differentiating amplifier 22 the combustion signal goes to a zero crossing Schmitt trigger type detector 24 which converts the fluctuating signal to pulses of differing duration, width, and spacing. Such pulses are transmitted to a one-shot monostable multivibrator 26 which includes a capacitor 28 and an adjustable resistor 30 connected to a stabilized source of constant voltage 32, for adjusting the pulse width duration of the output of multivibrator 26. The multivibrator input circuit-includes an edge amplifier gates 32 and 34.

The output pulses of the multivibrator 26 go to an integrator 36 by way of an adjustable resistor 38 constituting an integrator slope control. A capacitor 41 is connected in shunt with the integrator 36 and resistor 38, and the capacitor 4l is provided with a reset switch 42. From integrator 36 the signal goes to a one-bound comparator 39 by way of a buffer circuit 40. A sighting meter 42 is also connected by way of a meter driver 44 to the output of buffer circuit 40.

The output of comparator 39 goes to an adjustable delay circuit 46 having one selected voltage output going to a green or combustion OFF light 48, and another going to a red or combustion ON light 50. The comparator 39 is provided with a variable reference voltage circuit comprising an adjustable resistor or potentiometer 54 and a source 56 of direct current for comparison purposes. The DC level should generally be about 1.3 volts to 1.4 volts for the combustion ON condition; while a combustion OFF condition is about 1.0 volts to 1.2 volts or lower. The comparator 39 distinguishes and acts upon such levels causing the corresponding light to be energized, i.e., green: combustion OFF, and red: combustion ON, for example.

The delay circuit 46 acts to delay the actuation of either the red-combustion ON and green-combustion OFF lights 48 and 50, respectively. The delay is variable, and is a function of the particular burner being monitored, with the delay usually being about 10 to seconds.

Referring to FIG. 2, sensor head H, for detecting molecular carbon radicals, is suitably positioned with re- .spect to one burner of a pulverized coal fired multo the particular burner operating conditions of the flame being monitored.

The integrator 36 is provided with slope control adjustable resistor 38. The sighting meter 42 is connected to the output of integrator 36 by way of meter drive 44, and is calibrated to indicate the DC voltage thereof, i.e. 1.3 to 1.4 volts for combustion ON", and 1.0 to 1.2 volts for combustion OFF. The comparator 39 is provided with a comparative voltage supply circuit 52 that is adjustable by means of potentiometer 54.

The delay units allow time delays for flame ON flame OFF indication to be variable, and proportional to the burner fuel input rate. They comprise thermally actuated relay contacts. The integrator is an operational amplifier, having its input and output terminals connected together by an integrating capacitor 37. In this way the amplifier output is the time integral of the input signal. I

The. one-shot multivibrator comprises an integrated circuit which produces a predetermined length pulse at the output terminal each time the signal at the input to the AND gate 32 goes positive with respect to ground. Pulse length at the output is fixed by components 28 and 30. If an input signal goes positive during the active regime of the multivibrator it is ignored.

The sensor head includes the Cd.S photoconductive cell connected in a resistive bridge, the output of the bridge being differentially fed to an operational amplifier for voltage gain, and high common mode signal rejection. The signal from the voltage amplifier is then applied to a line driver so that the signal may be received remotely at the indicator equipment.

FIG. 3 shows a voltage/time recording of typical combustion OFF and ON signals and 82 at the output terminal A, FIG. 1, of the line driver 20 of the system, corresponding to the input of capacitor 23 by way of example.

FIG. 4 shows the output pulses 84 of the zero crossing detector 24, FIG. l, at terminal B thereof and the corresponding combustion ON complex input signal 82 at terminal A.

FIG. S-is an enlarged and exaggerated representation of the wave form 86 of the pulsed output of the monostable multivibrator at terminal C thereof, FIG. 1, showing variable mark to space ratio.

The reference (comparison) voltage level 88, and signal (combustion OFF) voltage level 90 are shown in FIG. 6. As can be seen in FIG. 1, the voltage readings were taken across points D, of the input of comparator 39.

At the output E, FIG. 1, of the delay 46, FIG. 1, the combustion ON/flame OFF voltage recordings are shown in FIG. 7, respectively, for the output E and delay 46 of FIG. 1.

The one-shot multivibrator 26 is triggered by positive going excursions (being of sufficient slope) from the combustion scintillation signal as sensed by the sensor 16. Because the peak detector or Schmitt trigger is intrinsically a zero-crossing detector, the output of the one-shot is derivative of the first differential coefficient of the input signal, due to the fact that the differentiating amplifier will attenuate signal components not due to combustible gases being evolved in the combustion front. The one-shot pulse length is increased or decreased as a function of burner primary and secondary air conditions, and also as a function of pulverized fuel particle size.

The analog integrator is used to sum the area under the individual one-shot'pulses. The DC level so derived was around 1.3 volts to 1.4 volts DC for a flame ON condition, while a flame OFF condition was about 1.0 volts to 1.2 volts DC or lower. The system is based on detecting radiation from chemiluminescent radicals and uses a standard cadmium sulfide detector unit, the maximum sensitivity of which is in the vicinity of .512 micron. The electronic signal conditioning can be summarized as follows: When the photocell output voltage reaches a certain threshold value and in addition is rising at a certain minimum rate, the zero-crossing detector is triggered, giving a positive change in the voltage output of the zerocrossing detector. When the photocell output voltage again crosses the threshold value but in the negative direction, the voltage from the zero-crossing detector is returned to its original value. The leading edge, or positive-slope part, of the zero-crossing detectors output is used to trigger the one-shot multivibrator, which produces a square-wave voltage pulse of constant duration and amplitude, but variable repetition rate. The output of the one-shot multivibrator is integrated with respect to time. If this integral falls within a certain range, which can be translated into the number of threshold crossings, positive fuel ignition is indicated.

The predominant frequencies detected by the sensing element in several multiple-burner coal-firing installations fall in the range of- 20-100 Hertz. By predominant it is meant the frequency at which the photocells output energy fluctuations are at a maximum. However, it must be noted that the photocell actually detects a very broad range of frequencies, some of which fall outside the range of response of the recording equipment.

The DC output from the integrator is applied to the one-bound comparator such that combustion ON combustion OFF levels can be distinguished and acted upon.

The variable delay appropriately delays the actuation of the green/red combustion ON/OFF lights. Delay is adjustable and is a function of the particular burner being monitored, but is usually around to seconds.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding useof other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

What-is claimed is:

l. A combustion detection system for pulverized coal fired burners, comprising:

a combustion sensor circuit for producing a high frequency output signal corresponding to radical radiation of the pulverized coal undergoing combustion at the mouth of the burner;

a differential amplifier circuit for differentiating such radical radiation signal whereby the latter is directly proportional to the sonic energy given off by the coal particles undergoing combustion;

a zero-crossing peak detector coupled to said amplifier circuit for converting the high frequency output signal thereof to pulses of varying duration corresponding to such sonic energy;

a one-shot monostable multivibrator connected to said detector for changing such pulses to one-shot pulses of uniform duration; 7 i an integrator acting to integrate such one-shot pulses into a direct current output, the voltage level of which corresponds in one range-to the OFF condition of such combustion, and in a different range to the ON condition thereof; a comparator for distinguishing between such ranges;

and true combustion ON and OFF indicators operated by said comparator as distinguished from flame detection per se of the burners. 2. A combustion detector system as defined in claim 1, in which means are provided for delaying the operation of said ON/OFF indicators by said comparator from 10 to 15 seconds. 3. A combustion detection system as defined in claim 2, in which said delay means comprises means for adjusting the duration of such delay to match the particular gas turbulancecharacteristics of the combustion of the 1 burner being monitored. 4. A combustion detection system as defined in claim 1, in which said sensor comprises a photocell which is sensitive to radiation at 0.512 microns wave length, said zero-crossing peak detector comprises a Schmitt trigger unit, and

said multivibrator comprises means for adjusting the p I duration of the output pulses thereof for optimum operation of the system in accordance with the H/F content of the output signal of the sensor. 5. A combustion detection system as defined in claim 4, in which i said integrator comprises means for adjusting the integrator slope for programming the system to handle combustion of relatively low'emissivity such as those present at start-up, as well asburners operating at low loads. 6. A combustion detection system as defined in claim 5, in which said integrator also comprises means for adjusting the integrator time constant for avoiding undesirable effects of gas turbulance in the combustion such as those due to the position of the combustion of the burner being monitored. 7. A combustion detection system as defined in claim 6, in which adjustable delay means are also provided for delaying the ,ON/OFF operation of said indicators by said comparator in case said integrator time constant cannot be made long enough to avoid the effects of undesirable gas turbulance in the combustion being monitored. 8. A combustion detection system as defined in claim 7, in which the sessor of molecular chemiluminescent carbon radicals includes a cadmium sulfide type photoconductive cell circuit responsive to the molecular carbon radical intensity variations produced by spatial movement of the combustion front of a pulverized coal burner subject to turbulance within the furnace containing such bumer; and the integrator provides an electronic memory such that when the flame front of the burning coal being monitored moves out of the field of view of the cadmium sulfide sensor the time constant of the integrator is such as to remember the flame ON condition until the combustion zone moves back into the field of view of the sensor.

9. A combustion detection system for pulverized coal fired burners having a zone atthe burner mouth from which pulverized coal particles undergoing combustion radiate short-lived chemiluminescent molecular carbon radicals, the first derivitive of the signal given off 10 cell for electrically differentiating the radiation given off by such radicals, whereby such output signal is directly proportional to the multi-source sonic energy given off by the coal particles undergoing combustion in such zone at the mouth of the burner.

10. The invention as defined by claim 9, including a zero-crossing peak detector circuit coupled to said sensor circuit for converting the high frequencey differentiated output signal thereof to pulses of differing duration, width and spacing, which are proportional to the multi-monopulse soud radiation fields given off by the burning coal particles in such zone.

11. The invention as defined by claim 10, including digital circuit means for converting such pulses to oneshot pulses of uniform duration, then integrating such one-shot pulses into a DC output having combustion ON and OFF levels, comparing such levels, and indicating the corresponding condition of actual combustion as distinguished from detection per se of the pulverized coal particles. 

1. A combustion detection system for pulverized coal fired burners, comprising: a combustion sensor circuit for producing a high frequency output signal corresponding to radical radiation of the pulverized coal undergoing combustion at the mouth of the burner; a differential amplifier circuit for differentiating such radical radiation signal whereby the latter is directly proportional to the sonic energy given off by the coal particles undergoing combustion; a zero-crossing peak detector coupled to said amplifier circuit for converting the high frequency output signal thereof to pulses of varying duration corresponding to such sonic energy; a one-shot monostable multivibrator connected to said detector for changing such pulses to one-shot pulses of uniform duration; an integrator acting to integrate such one-shot pulses into a direct current output, the voltage level of which corresponds in one range to the ''''OFF'''' condition of such combustion, and in a different range to the ''''ON'''' condition thereof; a comparator for distinguishing between such ranges; and true combustion ''''ON'''' and ''''OFF'''' indicators operated by said comparator as distinguished from flame detection per se of the burners.
 2. A combustion detector system as defined in claim 1, in which means are provided for delaying the operation of said ''''ON/OFF'''' indicators by said comparator from 10 to 15 seconds.
 3. A combustion detection system as defined in claim 2, in which said delay means comprises means for adjusting the duration of such delay to match the particular gas turbulance characteristics of the combustion of the burner being monitored.
 4. A combustion detection system as defined in claim 1, in which said sensor comprises a photocell which is sensitive to radiation at 0.512 microns wave length, said zero-crossing peak detector comprises a Schmitt trigger unit, and said multivibrator comprises means for adjusting the duration of the output pulsEs thereof for optimum operation of the system in accordance with the H/F content of the output signal of the sensor.
 5. A combustion detection system as defined in claim 4, in which said integrator comprises means for adjusting the integrator slope for programming the system to handle combustion of relatively low emissivity such as those present at start-up, as well as burners operating at low loads.
 6. A combustion detection system as defined in claim 5, in which said integrator also comprises means for adjusting the integrator time constant for avoiding undesirable effects of gas turbulance in the combustion such as those due to the position of the combustion of the burner being monitored.
 7. A combustion detection system as defined in claim 6, in which adjustable delay means are also provided for delaying the ''''ON''''/''''OFF'''' operation of said indicators by said comparator in case said integrator time constant cannot be made long enough to avoid the effects of undesirable gas turbulance in the combustion being monitored.
 8. A combustion detection system as defined in claim 7, in which the sessor of molecular chemiluminescent carbon radicals includes a cadmium sulfide type photoconductive cell circuit responsive to the molecular carbon radical intensity variations produced by spatial movement of the combustion front of a pulverized coal burner subject to turbulance within the furnace containing such burner; and the integrator provides an electronic memory such that when the flame front of the burning coal being monitored moves out of the field of view of the cadmium sulfide sensor the time constant of the integrator is such as to ''''remember'''' the flame ''''ON'''' condition until the combustion zone moves back into the field of view of the sensor.
 9. A combustion detection system for pulverized coal fired burners having a zone at the burner mouth from which pulverized coal particles undergoing combustion radiate short-lived chemiluminescent molecular carbon radicals, the first derivitive of the signal given off thereby being proportional to the multiple monopole acoustic energy generated by such pulverized coal particles undergoing combustion, comprising: a sensor circuit for producing a high frequency output signal corresponding primarily to such radical radiation of the pulverized coal undergoing combustion in such zone at the mouth of the burner, including a probe containing a photoconductive cell for viewing the particles of coal undergoing combustion in such zone of the burner, to pick-up such radical radiation, and differential amplifier circuit means connected to said cell for electrically differentiating the radiation given off by such radicals, whereby such output signal is directly proportional to the multi-source sonic energy given off by the coal particles undergoing combustion in such zone at the mouth of the burner.
 10. The invention as defined by claim 9, including a zero-crossing peak detector circuit coupled to said sensor circuit for converting the high frequencey differentiated output signal thereof to pulses of differing duration, width and spacing, which are proportional to the multi-monopulse soud radiation fields given off by the burning coal particles in such zone.
 11. The invention as defined by claim 10, including digital circuit means for converting such pulses to one-shot pulses of uniform duration, then integrating such one-shot pulses into a DC output having combustion ''''ON'''' and ''''OFF'''' levels, comparing such levels, and indicating the corresponding condition of actual combustion as distinguished from detection per se of the pulverized coal particles. 